Inductance device



- Patented May 2l, 1946 INDUCTAN CE DEVICE Anthony Mailinger, Astoria, N. Y., and Bruce E.

Stevens, Demarest, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application November 25, 1942, Serial No. 466,856

1 Claim.

This invention relates to an inductance device and particularly to a retardation coil for use in a filter for rectiiied alternating current.

An object oi' the invention is to improve the operating characteristics of an inductance device over a range of values of unidirectional current flowing through its winding.

Another object of the invention is to increase the inductance of an inductance device at a maximum value of direct current flowing through its Winding while maintaining at a high value the ratio o1' its inductance at zero direct current energization to its inductance at a maximum value of direct current energization.

It is common practice to supply current from a rectifier employing one or more grid controlled gas-illled tubes, for example, to a load through a iilter having one or more sections, each section comprising inductance in series with respect to the load and capacitance in shunt with respect to the load. When the alternating current supply voltage is steady and a iixed bias is applied to the grid or grids of the rectiiler tubeor tubes, each rectifier tube will pass space currentduring a portion oi a cycle of the alternating current supplied to the rectifier, that is, during a half cycle when the -grid is at a minimum negative potential and during one-quarter cycle when the grid is at a maximum value of negative potential. When the negative grid potential is increased beyond this maximum value, no space current ilows during any part of the cycle. In such an arrangement, the load voltage decreases with increase in load current.

In known arrangements for minimizing variations in load voltage, biasing voltage applied to the grid of a gas-illled rectifier tube is changed in accordance with changes in load voltage. The range of load voltage over which such a regulating arrangement is eilective is limited, however, since the period during which the rectifier tube passes space current can be varied only from onequarter to one-half of each cycle of the alternating current source. To improve the load voltage regulation it is desirable to employ in the ilrst filter section an inductance element the inductance of which is considerably higher for low values of load current than itis for high values oi' load current. However, it is also desir.- able that the inductance element have considerable inductance at high loads so that the filter will function to suppress alternating components of the current from the rectifier.

It is pointed out in United States Patent 1,876,451 to R. Gurtler, September 6, 1932, for example, that the inductance of an iron cored choke or transformer diminishes to a small value as the direct current through its winding is increased and that it is possibleto increase to a maximum value the inductance at a relatively high value of direct current by providing an airgap having a reluctance Rz such that the sum of Rz and R1 has a minimum'value of reluctance to alternating components of the flux, R1 being the reluctance of theiron portion of the core. In a choke coil or transformer so designed, however, the inductance of the device at relatively low values of direct current through its winding is approximately the same as the inductance at relatively high values of direct current.

In accordance with an embodiment of the invention herein shown and described for the purpose of illustration, an inductance device is provided with a core having at least two closed paths for the flux set up due to current ilowing in a winding of the device. The flux paths are prefer- 4ably separated by a sufiicient distance to cause the flux in either of saidpaths to be substantially independent of the ux in the other of said paths, the one path being a complete path of magnetic material and the other being of magnetic material except for a short gap which is devoid of magnetic material and which completely separates adjacent portions of the magnetic material in the path. In some cases, however, it is desirable to separate the flux paths by a shorter distance but in any device embodying the invention the distance should be greater than that for which the core has a maximum reluctance to flux due to constant direct current in the.winding. Specifically the inductance device comprises a three-legged core with a winding around the middle leg and the core comprises four sections made up of laminated magnetic material, the sections being separated by spacers of non-magnetic material. The laminations of the two outer sections are arranged so that no gap is formed in the magnetic paths while the laminations of the two inner sections are arranged to provide gaps in the magnetic paths which are shorter than the spacing between adjacent sections.

In the accompanying drawing,

Fig. 1 is a diagrammatic view of a circuit including an inductance device in accordance with the present invention;

Fig. 2 is an enlarged fragmentary view in perspective of the core of the inductance device shown in Fig. 1;

Fig. 3 is a plan view of a layer of laminations of the outer sections of the core of the inductance device shown in Figs. l and 2;

Fig. 4 is a plan view of a layer of laminations of one of the inner sections of the core of the inductance device shown in Figs. 1 and 2;

Fig. 5 is a plan view of a layer of laminations of another inner section of the core of the inductance device shown in Figs. 1 and 2; and

Figs. 6 and 'I consist of curves to which reference will be made in the following description o! the invention.

Referring now to the drawing, there is shown a rectifier I for rectlfying current from an alternating current source II and a illter circuit comprising a series retardation coil I2 and a shunt condenser Il through which current from rectiiler Iltis supplied to a load I4. The rectifier I l may be of the type employing gas-filled tubes the grid biasing potential of which may be varied to control the output of the rectifier. A regulator I5 connected across the load is provided for maintaining the load voltage substantially constant and circuit connections from the regulator to the rectifier are provided for impressing upon the grids of the gas-filled tubes of the rectilier a voltage set up in the regulator circuit I5. A regulated rectiller circuit of the type illustrated in Fig. i is shown and described in greater detail in an application of J. A. Potter and D. E. Trucksess, Serial No. 466,860, filed November 25, 1942 (Patent No. 2,377,370, June 5, 1945).

The retardation coil I2 comprises a threelegged core structure having a winding Il around the middle leg. The core is made up of laminations of magnetic material of equal thickness arranged in four sections 2|, 22, 22 and 2l adjacent ones of which are separated by spacers 25, and 21. respectively, of a non-magnetic material such as vulcanized fiber. Each of the outer sections 2| and 2l are made up of twelve T. laminations 2l, and twenty-four L laminations 29 or silicon steel. there being one T lamination and two L laminations in each layer. as shown in Fig. 3. 'I'he T and L laminations in alternate layers are reversed with respect to each other so that the butt Joints formed by the laminations of one layer are not in alignment with the butt joints formed by the laminations of adjacent layers. 'I'he ilux path for each of the two outer sections 2| and 24 of the core is a complete path of magnetic material. that is, the flux path hasmno airgap. or equivalent gap of non-magnetic material, which. if present, would need to be traversed by the flux in the path. Oi course there are minute gaps at the butt joints and between laminations which cannot be avoided but these gaps are negligible in so far as the present invention is concerned and may, therefore, be ignored.

Each of the inner core sections, 22 and 22, is made up of approximately forty-tour T laminations and eighty-eight L laminations of silicon steel. The T laminations I0 and L laminations JI o! section 22 are all arranged as shown in Fig. 4 to leave air-gaps at 22, 3l, Il and 25. The T laminations 40 and L laminations 4I of section 2l are all arranged as shown in Fig. 5 to leave air-gaps at l2, 4I, Il and l5. The air-gaps are preferably nlled with spacers of a non-magnetic material such as vulcanized liber. Thus no gap formed at section 22 is in alignment with a gap in section 23. Specifically, the length l of each of gaps I2, 32. Il. 35, 42. 41. 44 and 5 is .040 inch and the distance t of.each of spacings 25 and 21 is .0625 inch. The spacing 26 is also .0625 inch.

The curve z of Fig. 6 shows the relationship between the inductance of the retardation coil I2 and the direct current through its winding. As shown by the curve, the inductance at zero direct current is about l0 henries and the inductance at 1.2 amperes direct current is about 0.8 henry. The curve r shows the inductance which the inductance device would have il only the sections 2| and 24 having no air-gap were used as the core` The inductance would then vary from about 9.0 henries at zero direct current to about 0.1 henry at 1.2 amperes direct current. If only the core sections 22 and 22 which have air-gaps were used, the inductance would be about 0.7 henry at 1.2 amperes direct current and would be only slightly higher at zero direct current as shown by curve y.

The curves A and B of Fig. 7 show the relationship between the thickness t of each of spacers 25 and 21 and the reluctance of the core to direct current ux set up therein due to different amplitudes, respectively, of direct current flowing in the winding I6. It will be 0bserved that, starting with t equal to zero, as t is increased the direct current reluctance increases to a maximum value for a certain value o! direct current in the winding and then decreases, the direct current reluctance finally reaching a substantially steady value. For values of t less than that indicated by the vertical dash line C, the ratio of direct current reluctance with high direct current in the winding to direct current reluctance with low direct current is relatively small with respect to the ratio for values oi' t greater than that indicated by the line C. For values of t greater than that indicated by line C. the rdirect current reluctance shown by curve A falls much faster than that shown by curve B as t is increased. Therefore to obtain a large ratio of direct current reluctance with high direct current to direct current reluctance with low direct current, in accordance with the present invention, it is necessary to make t greater than that value of t for which the direct current reluctance is a maximum .rior a certain value of direct current in the winding. It has been found that, when the thickness t of spacers 25 and 21 is greater than the thickness indicated by the line C in Fig. 7, the inductance of the retardation coli I2 is much greater at low values of direct current through its winding than it is at relatively high values of direct current and that the inductance at high values of direct current is considerably greater than the value 0f inductance which it would have if only the sections without air-gaps were to be employed.

What is claimed is:

The combination with a retardation coil device. having a winding with a magnetic core1 of means for causing direct current the amplitude of which varies over a certain range to flow through said winding, said core comprising two separate sections providing two separate closed iiux paths. the first of said sections being of magnetic material and of relatively large cross-sectional area and having therein a series gap of fixed length devoid of magnetic material, the second of said sections being of magnetic material and of relativelyl small cross-sectional area and devoid o! any series gap, the self inductance of said device due solely to said first section being, for the uppermost part of said range, at least several times that due solely to the second section and, for the lower-most part of said range. a relatively small fraction of that due solely to the second section, the amplitude of the current within the upper portion of said range being suiiicient to at least partially saturate said second section.

ANTHONY MAJLINGER. BRUCE E. STEVENS. 

